HARVEST

While atmospheric dust has long been recognized as a key external iron source – a vital nutrient for photosynthesizing plankton – the contribution of hydrothermal iron, leached from volcanically active seafloor regions, remains largely unexplored. This is particularly true for shallow seamounts in volcanic arcs and hotspots, which potentially impact surface waters most directly. We will focus fieldwork on the Tonga-Lau region (2 x 35 days oceanographic expedition on board R/V Pourquoi Pas? scheduled end of 2027 + 1-year moorings + autonomous platforms etc.), known for its large phytoplankton blooms and a range of tectonically relevant settings. Findings acquired in the field will be extrapolated to the global scale, supported by advanced biogeochemical models, in order to simulate hydrothermal iron transport and chemistry, and to assess its role in primary production and the carbon cycle across regional and global scales. This research will reveal the previously overlooked impact of submarine volcanism on ocean fertilisation, offering new insights into the connections between solid earth, ocean dynamics, and marine ecosystems.